The selection of a suitable material for use as the first wall of a fusion reactor has been a continuing problem. One of the most serious problems associated with the first wall is radiation damage caused by the energetic neutrons emitted by the plasma. The neutrons cause irradiation hardening and also produce helium gas atoms within the matrix of a first wall material which collects on the grain boundaries of most structural alloys.
For this application, vanadium alloys have certain advantages compared with conventional structural materials such as stainless steels because they exhibit low residual activity after irradiation, high thermal conductivity and low thermal expansion. They also have good mechanical strength at high temperatures and good corrosion resistance when used with lithium, which has been proposed as a first wall coolant. However, these alloys are subject to radiation induced degradation of mechanical properties that comes from matrix hardening and from grain boundary embrittlement due to helium accumulation at the grain boundaries. Therefore, there is a continuing need to improve the resistance of vanadium alloys to these radiation-induced phenomena.